Method of casting slag



W. T. HURST.

METHOD OF CASTING SLAG.

APPLICATION FILED NOV. 29, 1919.

Patented Jan. 3,- 1922,

ENVEN'WMR FELL lTED STATES WILLIS T. BURST, or PITTSBURGH, PENNSYLVANIA,'Ass1G1ton. -To SLAG iaooxl MACHINE COMPANY, or PITTSBURGH,PENNSYLVANIA, A. congonarroit or PENNSYLVANIA.

METHOD or CASTING SLAG.

Patented Jan. 3, 11922.

Application filed November 29, 1919. Serial No. 341,478.

To all whom it may concern:

Be it known that I, VILLIS T. HURsT, a resident of Pittsburgh, in thecounty of Allegheny and State of Pennsylvania, have invented a new anduseful Improvement in Methods of Casting Slag, of which the following isa specification.

This invention relates to the handling of slag -'from blast furnaces.The particular objects of the invention are to handle such slag as fastas it is produced and drawn off, and in such manner that it is reducedin the handling to a hard dense product suitable for use as ballast forrailroads, the construction of streets and highways, as an ingredient ofconcrete, and in general any use to which broken stone or gravel may beput. In general the method consists in cooling the slag quickly in thinlayers, said layers being of a predetermined thickness depending on thetime available for cooling. The latter element in turn depends on thetime elapsing between flushings of the furnace.

Furnace slag is disposed of in a number of different ways. For exampleit is reduced to granular form by plunging it into water. Or it may betransported in slag cars to a dump, where it is allowed to cool normallyin the air. This results in a slag that is light and porous. Bythe-method of the present invention slag is sotreated that when cold itis reduced to a dense hard mass having very nearly the physicalproperties of stone, and therefore useful for purposes to which crushedstone may be applied.

The drawings show diagrammatically a form of apparatus suitable forcarrying out the method. Fig. 1 is a plan view of a layout suitable forcooling slag from a single blast furnace; and Fig. 2 is a verticalsection on the line 2-2 of Fig. 1.

The slag is led from a furnace by a runner. In the present case thisrunner is divided into troughs 1 and 2, the first of which is used toreceive slag when taking a cast from the furnace while the other, 2, isused to receive slag when it is tapped off from the cinder notch. In therunner 1 is a separator 3 which serves to catch any molten iron that maystill remain in the slag. This is necessary in order to prevent theburning of the molds or pans hereinafter described and also to preventthe slag from sticking thereto. The slag overflows into the runner 4,which communicates with branch runners 5 and 6. These branches carry themolten slag to the several-cooling receptacles below described. A gateor deflector 7 is placed at the point where the runner 4 enters thebranches 5 and 6, and this may be used to direct the necessary quantityof slag into each branch. A wall 8 forms a pit which is preferablydivided by cross walls 9 into a series of compartments 10 in each ofwhich water is maintained at a predetermined height. A series ofreceptacles 11, formed of sheet metal or the like, are floated in thesecompartments. These receptacles may be in the form of pans, molds orboxes, and preferably are of such dimensions that four of them will takeall of the slag coming from a single flushing of the furnace withoutgetting too great a depth of slag in each pan, although differentnumbers may be used.

Preferably these receptacles are in the form of pans, having their sideand end walls flared slightly, so that the solidified slag will bedischarged therefrom when they are turned upside down. These pansnormally float in the tanks 10. The branch runners or gutters 5 and 6extend along the tops of the dividing walls 9 to substantially midwaythereof, and at their ends are provided with spouts 12,which projectover the edges of the dividing walls and into position to discharge themolten slag into the middle portions of the receptacles 11, asillustrated. At the junction of each of the spouts 12 with the branchrunners is a de flector or valve 13, pivotally mounted at 14 andprovided with a handle or other operating means 15, so that it can bemoved into either of two positions, to direct the flow of molten slagfirst into the pan or receptacle on one side of the dividing wall andthen into the pan or receptacle on the other side. The molten slag isrun into one receptacle until that is filled to the desired depth, andthen it is deflected and caused to flow into the other pan. As the panis loaded it gradually sinks into the water until it comes to rest uponsupports 16 in the bottom of the compartment 10. The height of the panis such that when it has settled down upon'these supports it will not besubmerged, but will be surrounded by water on its bottom and all sides.By this means the receptacle and its contents are a dump and thereinverted.

subjected to a very rapid cooling. As soon as a solid crust forms overthe top of the slag, water may be played over the surface by means ofspray nozzles 18 from water pip-es 17 which are placed along the sidesof the transverse walls 9. \Vater is not admitted to the spray pipesuntil the top surface of the slag has been solidified, and therefore theslag is not granulated by contact with the water as would be the case ifthe water were sprayed while the slag is in molten condition.

By this means, the water cooling of a comparatively thin sheet of slagexposed over its entire under surface to water cooling, and by playingwater over its solidified upper surface, there is produced a quickcooling of the entire mass of slag. The result is that the mass sets ina dense, solid, hard form, and not in a porous or spongy mass such asresults when such material is allowed to air cool.

\Vhen the slag is solidified the pans are removed by any suitable means,and taken to The solidified slag will drop out, due to contraction fromcooling and because of the tapered shape of its containers. It is thenbroken into pieces and crushed to any desired size and can be utilizedin many ways.

To produce this hard rock like slag by the present method, and in suchmanner as to continuously take care of the normal flushings of a blastfurnace. there are three elements to be considered. These are the timeavailable for cooling the slag. the depth to which it is poured in thecooling pan, and the temperature to which it is exposed.

Slag is made continuously in the reduction of ore to metallic iron andcollects and rests upon the liquid iron in the hearth of the furnace.\Vhen sufiicient slag has been made it reaches the cinder notch which islocated above and to the side of the iron tap-hole. The slag hole isopened and the accumulation of slag above the cinder notch is drawn off.This process is repeated two or more times between each cast of iron.'hen the iron tap-hole is opened the liquid iron is drawn off and as theiron nears the end of the drawing off or casting period slag below thelevel of the cinder notch follows the iron through the iron tap-hole andis deflected from the path of the molten iron to the slag runner bymeans of a skimmer. The volume of slag following the iron at a cast islarger than the fiushings between casts. The intervals between castingsand tlushings vary somewhat at different furnaces but the normal timebetween flushings is forty-five minutes minimum and two hours maximum.The longer time elapses between flushings taken just after a cast ofmetal has been made from the furnace. and the minimum time is justbefore a cast is made. In order to be commercially practical, thisprocess of handling slag and rcducing it to a particular form, must becapable of taking care of a flushing of slag in a period of less thanforty-five minutes. The average temperature of the water in thispractice will be approximately 150 Fahr. and the temperature of themolten slag is nearly constant and averages close to 2500 Fahr.

In the present method the thickness of the layer of slag poured intoeach pan is varied according to the time that is available betweenflushings of the furnace. For example, when the next flushing is tooccur forty-five minutes later, the slag is run into the pan in acomparatively thin layer, three to four inches; whereas if two hours areavailable it maybe run to a depth of approximately six inches. In thelatter case the time necessary for solidification of the slag is muchlonger, I have determined by experiment that a layer of slag exposed towater cooling as described in this specification when poured to athickness of four inches will require approximately thirty minutes tosolidify. A thickness of six inches will require approximately ninetyminutes to solidify, and a thickness of nine inches will requireapproximately five hundred and forty minutes to solidify. Therefore itis evident that the thickness of the layer must be varied according tothe time that is available for solidification, that is before the slagmust be removed to make place for the next flushing.

Consequently. in the practice of this method the slag drawn off atcompletion of a cast from the furnace will fill the pans to a depth ofnearly six inches. and there is available nearly two hours before thenext flushing will normally occur. This slag will have been solidifiedand may be removed after an hour and a half. As the time between normalflushings grows smaller. untiljust before the next cast it isapproximately forty-five minutes. the layer of slag poured will be' madeless. so that the last one will be four inches deep. or may be less. Inthis latter case it will have been solidified and may be removed afterthirty minutes.

Thus in the practice of this method the three elements of depth of layerof slag.- time of exposure to cooling. and temperature to which exposedhave to be considered. The initial temperature of the slag is nearlyalways the same. and the temperature of the water may be consideredconstant. (onscquently the depth of layer and time of exposure are theelements 'aried. Andparticularly the thickness is varied with the timeelement.

The pans themselves are made considerably deeper than is necessary fortaking care of a four to six inch layer of slag. This is done for tworeasons. First in order to prevent any water in the pits from flowingover the tops of the pans when they have settled down onto theirsupports, and second in order to be able to take care of an excessamount of slag such as occasionally results when the cinder notchbecomes plugged and the excess of slag has to be drawn off through theiron notch of the furnace. This, however, has nothing to do with thenormal practice of the invention.

I claim:

1. The method of treating molten slag t0 producea dense hard slag,consisting in pouring the molten slag into a shallowmeceptacle or mold,water cooling said receptacle or mold, and when the surface of the slagin said receptacle or mold has solidi fied, introducing water onto saidsurface, thereby quickly cooling the entire mass.

2. The method of treating molten slag to produce dense hard slag,consisting in separating any iron from the slag, pouring the molten slaginto a pan or receptacle, and water cooling said pan or receptacle tothereby quickly cool the slag.

In testimony whereof, I have hereunto set my hand.

WILLIS T. HURST.

Witnesses:

ALICE A. TRILL,

HOWARD L. SNIVELY.

